Measuring viscosity of a material is an indispensable technique for quality control, performance evaluation, material control, research and development in manufacturing process of medicament, foods, coatings, inks, cosmetics, chemicals, papers, adhesives, fiber, plastics, beer, detergents, concrete admixture, and silicone or the like. As the methods of measuring the viscosity of such product, there is a method using a capillary tube, a method by making an oscillator contact a sample, a method using a rotator, and so on.
One of the methods using a rotator among the above-mentioned methods is disclosed in an after-mentioned Patent literature 1. The technique is configured so that a conductive rotator (sphere) is sank in a sample container containing a sample liquid, and a rotating magnetic field is given to the rotator from an outside of the sample container. At giving the rotating magnetic field, the electric current is excited in the rotator by the rotating magnetic field. The rotator rotates caused by the interaction of Lorentz force between the electric current and the rotating magnetic field is given to the rotator. At this time, the rotating speed of the rotator gets lower than the rotating speed of the rotating magnetic field according to the viscosity of the sample liquid. The viscosity can be calculated by means of such lag of the rotating speed. That is to say, a relation of the rotating speed of the rotator and the difference between the rotating speed of the rotator and the rotating speed of the rotating magnetic field can be expressed by a linear equation, and a slope of the linear equation becomes the viscosity.